Titanium dioxide pigment

ABSTRACT

This invention relates to titanium dioxide pigment of improved photochemical resistance which contain alumina and has a surface coating of a mixture of hydrous oxides of aluminum, silicon and zinc. The resulting pigment possesses improved resistance to discoloration and chalking upon exposure to ultraviolet light and is particularly useful as a pigmenting material for coating compositions and for opacifying resinous materials including laminates which are conventionally used in wall coverings, counter tops and cabinet facings.

United States Patent Sheehan 51 Feb. 8, 1972 [54] TITANIUM DIOXIDE PIGMENT [63] Continuation-impart of Ser.' No. 636,628, May 8, 1967, Pat. No. 3,528,837.

52 user "106/300, l06/308B [51] lnt.Cl v ..C09cl/36 [58] Fieldof Search ..l06/300,308B

[56] Reierences Cited UNITED STATES PATENTS 3,418,147 12/1968 Fields [06/300 Primary Examiner-James E. Poer Attorney-Roland A. Dexter [57] ABSTRACT This invention relates to titanium dioxide pigment of improved photochemical resistance which contain alumina and has a surface coating of a mixture of hydrous oxides of aluminum, silicon and zinc. The resulting pigment possesses improved rcsistance to discoloration and chalking upon exposure to ultraviolet light and is particularly useful as a pigmenting material for coating compositions and for opacifying resinous materials including laminates which are conventionally used in wall coverings, counter tops and cabinet facings.

3 Claims, No Drawings TITANIUM DIOXIDE PIGMENT of hydrous oxides of aluminum, silicon and zinc. The resulting: pigment possesses improved resistance to discoloration and i chalking upon exposure to ultraviolet light and is particularly useful as a pigmenting material for coating compositions and for opacifying resinous materials including laminates. which are conventionally used inwall coverings, countertops' and cabinet facings.

Titanium dioxide pigments have the coloring and opacification of resins and, in particular, melamine-formaldehyde, urea-formaldehyde, and.phenol-fo'r maldehyde resin. Such resins are used in preparation of found wide application: I I

tice of the present invention that the crude TiO, pigment have associated therewith, either by formation in situ or subsequent addition prior to calcination or oxidation, a small amount of aluminum oxide, preferably'about 0.1 to 4.0 percent based on the weight=of the TiO pigment.-

Thus, one method of obtaining a crude TiO pigment material for'usein the present invention is by the digestion of titaniferousmaterial such as ilmenite with a strong mineral acidsuch as sulfuric acid; whereby there is obtained a-soluble titanium'salt; As'is well known, thetitanium'salt is converted to atitanium dioxide composition by controlled hydrolysis, and' resultant hydrolysates-arefiltered, washed and calcined.'Calcination yields a'material which can serve in many I conventionalpigrnentary applications.

' Forthepurpose of-the present invention, as stated above, it

v is necessary that the crystalline rutile 'IiO, be cofonned with a small amount of'aluminu'm oxiderutile; The aluminum oxide can be addedas an aluminum salt or hydrous aluminum oxide to the filteredand washed'hydrolysate prior to the calcination step: ,Likewise,-': the TiO 'pigment which is useful as a starting I material'in the present invention can be obtained by commolded articles andmorewidely used'in the preparation of laminates wherein the resin acts as an adhesive'to bind together layersof materials in such as wood and paper: The laminates which are prepared in this form are highlydurable materials with good structural strength and'ar'e commonly found in counter tops, shelving and wall covering products. These products are typically eoloredwith pigrnentary materials which are compatible with both the resin and the laminar components. Titanium dioxide pigment which is typically used for opacifying such resinous'compositions possesses excellent opacifying properties but is prone to discoloration and degradation upon exposure to ultraviolet light.

Efi'orts have been made to provide titanium dioxide pigments which could be used in resinous compositions for the above-noted purposes-to provide the desired opacification while remaining resistant to discoloration and degradation fective, it must be conducted at a-temperature of over about 700 C. The requirement for the extra calcination step is undesirablefrom'the standpoint'of production costs and, even' more importantly, because high-temperature variation in the calcining apparatus results in the production of apigmentary product of poor'dispersibility and optical properties.

In view of the importance of titanium dioxide pigment'and the widespread use thereof in applications requiring light-stable pigrnentary materials, it is an object of the present invention to provide an improved pigrnentary material which has excellent photochemical resistance and is thus usable for ap,- plications involving exposure to ultraviolet radiation. It is a further object of the present'invention to provide Ti0 pigment of improved photochemical resistance which can be used in resinous substrates such as those formed'by forr'naldehyde condensation with melamine, urea, or phenol! Irr par ticular, it is an object of the present invention to'provide a' light stable TiO pigment which is prepared by treating a crude TiO pigment'obtained by cocalcining or cocombusting a titaniferous material with an aluminum containing material,

with a mixture of hydrousoxides of aluminum, silicon and' The present invention provides light-stable TiO, pigment byusing TiO, which is derived either from conventionalhydroly sis or combustion processes. However, it is critical tothep'racbustion of titaniferous salts such as titanium tetrachloride. Suchcombustion-methods for obtaining TiO pigments are well known and the choice of anyparticular technique is not an essential part of the present invention. It is a matter of choice'whether the-aluminum oxide is incorporated into the TiO, starting material by formation in situ or by addition during the combustion of'a titanium compound. It is most convenient to addan-aluminum-containing material to obtain formation in situ, for example, an aluminum salt such asaluminum chloride is mixed=with thetitanium tetrachloride andbumed concurrently-to eoforma Ti0 -Al O crude pigment.

Regardless-of the means-by which the titaniaalumina crude pigment is obtained, it can be converted by the process of the present invention to a pigrnentary material of improved photochemical resistance. It is noteworthy, however, that the substitution of other oxides such as magnesium oxide for alumina does'not-yield a pigment of improved photochemical resistance such as can be obtained by the practice of the present invention; This is not to say, however, that auxiliary materials cannot be presentin the starting material. Thus, it is feasible to have-present in the starting material, additives such as carbonates andoxides of phosphorus which, to a large extent, provide desirable properties with respect to 'color brightness and tinting strength. However, it is to be understood that the present invention can be practiced without the addition of these auxiliary materials.-

Theadmixture-of the hydrous oxide coating onto the TiO, pigment maybe carried out by any one of several methods. All the hydrous oxides may be coated upon the rio Ano, pigment simultaneously-or the coating-may be accomplished by sequentially applyingeach oxide coating. A convenient way of practicing th'e present invention involves formingan aqueous solution 'of "a soluble silicate, asoluble aluminum salt, and a soluble zinc-salt, admixingtheresulting' solution with the TiO A1 05 pigment, and then neutralizing the resulting slurry to a pl-i in therange of about 6 to 9, whereby-the soluble salts are converted to: their respective hydrous oxides which are deposited asa'coating on the TiO, particles. The neutralized slurry'can be filtered and washed directly,- orit may be aged prior tofiltration and washing. After washing to remove soluble salts; the filter cakemay be further treated, driedand then pulverized to give the finely di'vided pigment of the present invention. Various'solublealuminum, silicon and zinc salts may be usedto deposirthe hydrous oxide coating provided by the present invention. Conveniently, aluminum sulfate can be used to supplythe-aluminum content required by'the treating solution of-the present invention. Soluble silicates such as an alkali metal" silicate, e.g., sodium silicate, may be used to supply"thesilicacontent anda'soluble-zincsalt such as zinc sulfate-may be used to supply the zinc-oxide content of thetreatingsolution used in the presentinvention. The treating sured as silicon dioxide, and between about 0.05 to 10 percent, preferably 0.1 to 0.5 percent of the zinc compound measured as zinc oxide, all of which are based upon the weight of Y the O -A1 0 to be treated. The limits are derived as a consequence of experimentally determining the regions within which the advantages of the invention are obtained.

The coated o -A1 pigment produced by the present invention will be found to have a high degree of light stability and, surprisingly, the light. stability is imparted without the requirement that the coated pigment be recalcined at a high cake was dried at 110 C. and disintegrated in a laboratory micropulverizer.

EXAMPLE 3 No A1 0 Pretreatment,With Calcining The sample was processed in the same manner as Example 2 up through the drying step. After drying, vthe sample was passed through a 4-mesh Tyler screen to break up lumps and fluid-energy milled'in a 2-inch reductionizer with superheated steam at 500 F. The milled sample was then given a heat treatment at 750 C. for the one-half hour and subsequently disintegrated in a laboratory micropulverizer.

EXAMPLE 4 temperature. it should be noted that a recalciningtreatment, Y i.e., partial to complete dehydration of the hydrous oxide Coformed T f 'f i End Treatment coating, will effect some improvement in light stability of the washed mama hydrolysaie comamulg a small amount of pigment while causing slight deterioration of other pigmentary me se ed l! was blended percent Kzcoar properties. Suitable recalcining temperatures are from 400 to sufficient Hapo4 to gwe percent P percent 800 C. which results in up to about 90 percent dehydration. A1203 as the sulfate base? on the T102 equowalem of h Nevertheless, a pigment can be obtained which has excellent hydrolysate and calcined at about 9 to a i light Stability without a calcining posmeatmgm. content of at least 99.5 percent as determined by X-ray dif- The present invention thus provides a TiO pigment which fraction allalysls' The calcmer dlscharge was processed has excellent light stability in the content of resinous coating to completion as the Example compositions. Pigment can thus be advantageously incor- EXAMPLE 5 porated into melamine-formaldehyde, phenol-formaldehyde and urea-formaldehyde resin compositions, or alternatively, it Present invention can be used with advantage in fiber compositions as an opacicalcined z' z a as P p in Example 4 was finished fying agent or for the purposes of delustering the fiber. y blending, -r as in Example 2 after hydi'ociassification Thefollowing examples are presented to further illustrate to eliminate D coarser man 4 micronsthe present lnvennon. EXAMYLE 6 EXAMPLE 1 Present Invention and Calcining Step Control Calcined O -A1 0 prepared in Example 4 was treated Washed tltanla hydrolysate, containing a small amount of with hydrous oxides as in Example 2 and the fl id -gy rutile seed (2.5 percent as described in Example 2 of US. Pat. mined and heat treated as in Example 3 No. 2,494,492) was blended with 0.4 percent K CO sufficient H PO to give about 0.26 percent P 0 and 0.02 percent EXAMPLE 7 MgO (as the sulfate), based on the "no, equivalent of the 40 Coformed m- 2 3 y Oxidation-N0 End Treatment hydrolysate, and then calcined at about 1,000 C. to a rutile Ruiiie z cofol'med with 2 3 through the combustion of content of at least 99.5 percent as determined by X-ray dif- Ticie g with Oxygen in the Pissehce of gaseous aluminum fraction analysis. The subsequent caiciner discharge was then chloride in amount of Percent 2 3 the z pulverized in a hammer mill such as the micropulverizer and, equiviiieht of the Ticid was Processed as described in Example after slurrying water to yield a 20 percent by weight slurry, i smihswith slurrying in 2 at about a 20 P y deflocculated by adjusting the pH of the slurry to 9.0-100 welghtsolld content with sodium hydroxide. The slurry was then settled for a suffi- EXAMPLE 8 cient time to separate particles coarser than about 4 microns in and the fines were then flocculated with a suitable reagent Present invention-Chloride Pigment such as MgSO The slurry was then filtered and dried to 1 15 Rulile 2' 2 s as described in Example was end treated C. and disintegrated in a laboratory micropulven'zer. with hydrous oxides and finished y g? etc, as in EXAMPLE 2 ample End-treated Control-No A1 0 in TiO Starting Material EXAMPLEQ This sample was processed in the same manner as Example NO Zinc Oxide in End Treatment 1 up to the flocculation of the fines. In this case, the fines were Rutile 1 o as described in Example 4 was end biended" with P 2 3 as -26 4 Percent treated with 2.0 percent A1 0 1.0 percent Ti0 and 1.0 perz as e a and Percent Zho as Zhsoi a 2 cent Si0 as the hydrous oxides, neutralized, washed and dried sis. T e lurry was e heated to C. (although y as in Example 2, then fluid-energy milled, but not heat-treated perature from 25 C. to the boil may be used) and adjusted to 60 as in Example 3 neutral P with ammonium y The neutral Following is a tabulation of the various examples and the ized slurry was then filtered and washed. it may be mixed for h h i l resistance f h pigments as d i d i y desired length time Prior to filtration and washingmandelic acid and glycerine. The description of the test After washing to substantially remove the soluble salts, the procedure f ll th bl TABLE I Hydrous oxide Post end treatment Reflectance Percent Example Description treatment Milling calcination Initial Final drop 1 Calcined with 0.02% MgO and then hydro- None Micro-pu1verizing None 86.0 3. 22,2

' classified.

d i' g' 3 6 rMicr ulverizi N 2 o or: o-p ng---.. one 86.0 76.4 9.6

4.0% Ai20a-- 3 .do --{2.0% SiOz ..}Jetmilled /houratt| C 85.3 84.3 1.0

TABLE I Reflectance Hydrous oxide Post end treatment Percent Example Description treatment Milling calcination Initial Final drop 4 Calcined avith 0.30% A1203 and then hydro- None Micro-pannin None 86.0 73.4 7.

classifie 4.0% A1203 I 5 do 2.0% SiOz ..}Mr0-pulverizing None 86.0 85.2 0.3

. 3% ZnO 4.0% A1203 6 .d0 Jetmllled hourat750 C. 85.9 85.4 0.5

. l1 7 TiCh combusted with O2 in pr scence of 3.0% Non e Micro-pulverizing None 84.4 71.4 13. 0

A1203 as A101; hydroclassified.

4.0%.A12OL 8 do 4. 2.0% SiOz Mlcro-pulverizing None 85.5 82.5 3.0

as- 9 Hydrolysate calcined with A120; and then a hydmflaSS-Lfim igi'; T 1 022 Jetmilled None 87.0 81.4 5.6

I EST PROCEDI R E MgO-treated with 4% A1,o,. 2.0% sio, and To 10 grams of test sample add 4.5 cc. of a 7 percent solu 9-3:: ZhO-micropulver- 90 7 68 2 22 5 m tron of mandelrc acrd n glycerrne. Mix thoroughly to give a Example 3 Same as (2) except paste suitable for mulling, but in the event a very still paste is fluid-energy milled encountered, a few more drops of glycerine may be added i gg pg z 900 830 70 OI our. without materially affecting the results. Mull the mixed paste. Example 5 calcined with 03% Transfer a portion of the paste to a clean glass slide, spread o and treated as paste evenly over the surface and cover with a second slide. 25 (2% Wipe off excess paste and bind the slides together. Enough paste must be used to prevent transparency or pin holes in the finished slides.

Using a standard reflectometer, initial green reflectance readings of samples are taken. Place slides equidistance apart on a rotating disc so that each will receive the same amount of UV. irradiation. Expose rutile pigments for 5 hours. Measure and record drop in reflectance.

The drop in reflectance is a measure of photochemical stability. Each test pigment should be compared against a known standard prepared in the same manner.

Reported values will be percent drop in reflectance at the end of the 5 -hour exposure.

EXAMPLE l0 Melamine Resin Containing Pigment of the Present Invention Samples prepared as described in Examples 2, 3, and 5 were evaluated for their light stability in a melamine formaldehyde resin by exposing the pigmented resin films in a UV. Weathero-Meter for l 6 hours.

The following results were obtained:

TABLE II TA-68 Cymel Resin Sample Description Initial Final k Drop Example 2 calcined with 0.02%

1. Pigment particles having cores of crystalline rutile titanium dioxide containing from 0.1 to 4.0 percent alumina, said cores having a coating thereon consisting of hydrous oxides of aluminum, silicon and zinc in amounts providing from 2 to 10 percent A1 0 from 0.5 to 10 percent SiO- and from 0.05 to 10 percent ZnO, said percentages being by weight based on the Tio -Al O core. a

2. The pigment of claim 1 wherein the hydrous oxide of A1 0 is'present in from 3 to 6 percent, the hydrous oxide of SiO is present in from 1 to 3 percent, and the hydrous oxide ofZnO is present in from 0.1 to 0.5 percent.

3. The pigment of claim 1 wherein the coating is up to about percent dehydrated.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5, 640,745 Dated February 8, 1972 Invntor(s) Gerard Martin Sheehan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 41 after the word dioxide pigment should be added.

Column 3, line ll,"TiO Alo should read TiO -Al; '=0

Column 4, line 50, "Example was" should read --Example 7 was Column 6, line 30, '2.0 percent and" should read 2.0

percent SiOg and Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK attesting Officer USCOMM-DC BO376-F'69 U.S. GOVERNMENT PRINTING OFFICE: I969 O366-33 FORM PO-1050(10-69) 

2. The pigment of claim 1 wherein the hydrous oxide of Al2O3 is present in from 3 to 6 percent, the hydrous oxide of SiO2 is present in from 1 to 3 percent, and the hydrous oxide of ZnO is present in from 0.1 to 0.5 percent.
 3. The pigment of claim 1 wherein the coating is up to about 90 percent dehydrated. 